Cooling system, employing heat-expandable means, for an aerodynamically heated vehicle

ABSTRACT

A cooling system for an aerodynamically heated vehicle includes a chamber disposed within the vehicle and containing a coolant and a heat-expandable means for increasing the pressure and reducing the volume within the chamber upon being heated during aerodynamic heating of the vehicle. Coolant under pressure exerted within the chamber by the expandable means is ejected from the chamber and conducted to the external surface of the heated, external skin of the vehicle. In one embodiment, a plurality of coolant chambers are disposed within a vehicle, each being positioned adjacent a respective portion of the outer skin of the vehicle for providing independent protection of each portion.

United States Patent [191 Stalmach, Jr.

[ 1 COOLING SYSTEM, EMPLOYING HEAT-EXPANDABLE MEANS, FOR ANAERODYNAMICALLY HEATED VEHICLE [75] Inventor: Charles J. Stalmach, Jr.,Grand Prairie, Tex.

[72] Assignee: LTV Aerospace Corporation, Dallas,

Tex.

221 Filed: May 25,1971 21 Appl.No.:1 46,703

[52] US. Cl 244/1 SC, 102/105, 244/117 A I 3,103,885 9/1963 McLauchlan244/117 A 51 Jan. 15, 1974 Primary ExaminerMilton Buchler AssistantExaminer-Barry L. Kelmachter Attorney--James M. Cate [57] ABSTRACT Acooling system for an aerodynamically heated vehicle includes a chamberdisposed within the vehicle and containing a coolant and aheat-expandable means for increasing the pressure and reducing thevolume within the chamber upon being heated during aerodynamic heatingof the vehicle. Coolant under pressure exerted within the chamber by theexpandable means is ejected from the chamber and conducted to theexternal surface of the heated, external skin of the vehicle. In oneembodiment, a plurality of coolant chambers are disposed within avehicle, each being positioned adjacent a respective portion of theouter skin of the vehicle for providing independent protection of eachportion.

13 Claims, 10 Drawing Figures PAIENIEU A $785,591

SHEU 1 0F 3 CHARLES J. STALMACH, JR. F/G 3 INVENTOR BY 9W). w ATTORNEYPATENTED 3,785.591

SHEET 2 BF 3 FIG 7 CHARLES J. STALMACH, JR.

INVENTOR ATTORNEY Pmmwmsmm 3,785,591

SHEET 3 [IF 3 INVENTOR ATTO R N E Y CHARLES J. STALMACH, JR.

COOLING SYSTEM, EMPLOYING HEAT-EXPANDABLE MEANS, FOR AN AERODYNAMICALLYHEATED VEHICLE This invention relates to cooling systems for vehiclessubject to aerodynamic heating during high speed, atmospheric flightand, more particularly, to such cooling systems which are operable inresponse to aerodynamic heating.

In the design of high-speed aircraft and space vehicles, a majorlimiting factor has been the difficulty of protecting such vehicles fromdamage or destruction from the effects of frictional and radiational,aerodynamicheating during hypervelocity flight through portions of theatmosphere of the earth or other planets. This so-called heat barrierbecomes an increasingly serious problem at velocities above Mach 4 or 5and is a particular problem in the development of shuttle vehiclescapable of operation in both a conventional, aerodynamic mode within theatmosphere of the earth and in rocket-powered mode outside theatmosphere. A design requirement for such vehicles is that they be ableto, upon entering the atmosphere, to manuever to a landing area byconventional, aerodynamic flight, utilizing wings and aerodynamiccontrol surfaces. These wings and control surfaces must therefore bepreserved during reentry to ensure safe operation of the vehicles duringrelatively low-speed, atmospheric flight. For this reason, the vehiclesmust be protected against thermal damage of external surfaces or loss ofstructural integrity. Other examples of vehicles subject to damage fromaerodynamic heating include missiles which reenter the atmosphere atvery high velocity and are decelerated by pressure and frictionalresistance of the at mosphere, the nose portion of such missiles beingsubjected to intense heating. Additionally, thermal damage is of concernwith respect to airplanes designed to fly in the atmosphere at speedsabove Mach 3-5 for sustained periods of time, because the deleteriouseffects of aerodynamic heating may also occur as the temperatures ofaircraft components build up over extendeo periods during flight at suchvelocities.

In the past, various solutions to the problem have been proposed. Theone normally employed for the protection of missiles during reentry isthe use ofa heat shield which insulates the forward portions of avehicle from severe heating by partial ablation, reradi'ation, andabsorption. Such an approach does not .lend itself to usage in a vehiclealso capable of conventional, aerodynamic flight through the atmosphere,however, bacause any ablation or fusing of external portions of thecraft may distort the external configuration of the vehi cle and resultin a loss of aerodynamic control and an increase in drag. Also, it wouldbe very expensive to refurbish the ablated surfaces after each useduring repetitive usage. An approach which has been used at lowervelocities is the circulation of a coolant through passageways adjacentthe most severely heated portions of an aircraft, such as the nose andthe leading edges of the wings, the coolant acting to distribute theheat throughout the craft and thus cause it to be partially disbursed inheat-sink fashion. Such systems are not satisfactory at very highvelocities, however, where much greater cooling capacity is required. Itis generally proposed to provide the necessary increased coolingcapacity by the conduction to a coolant of energy from the severelyheated, external surfaces of a vehicle and then the ejection of thiscoolant from the vehicle through porous, external elements for furthercooling the heated portions. Coolant ejected thusly by transpirationthrough a porous material provides cooling during the evaporation of thecoolant and by the formation of aboundary layer of vaporized coolant forshielding the external surfaces from adjacent, superheated, gaseousflow, as will be more fully described hereinbelow. A relatively smallamount of fluid for affording a limited degree of evaporative coolingmay be suspended immediately adjacent an external wall portion, e.g.,within a structure containing a layer of coolant adjacent to thewall-portion. Or, a larger amount of coolant may be contained in achamber within the vehicle and ejected from the vehicle to heatedportions of the external skin. Ejection of the coolant may also beaccomplished through suitable orifices preferably formed forwardly ofrespective, heated areas of the skin, or it may be accomplished bytranspiration of coolant through a porous element contiguous with arespective heated area of the skin, as indicated above.

Prior-art systems of the type wherein a coolant stored in a tank in avehicle is caused to flow to a heated, external surface of the vehiclehave employed various types of heat sensors and control systems toactivate pumps or other pressure sources for causing ejection of thecoolant upon the occurrence of deleterious heating. Such controlsystems, pumps, meters, and the like add undesirable complexity andweight to the cooling system and are subject to possible malfunction orfailure under stress. In an alternate approach, coolant contained aboardthe vehicle is ejected by pumps or other means actuated in accordancewith a predetermined program dependent upon flight timehsuch a method isnot preferable for most applications, however, in that heating effectsmay not occur as predicted, and thus, the program may not correspondwith actual conditions experienced by the vehicle. Furthermore, such asystem also requires the use of fairly complex circuitry and controlsystems which, again, are subject to failure or malfunction.

It must be recognized that reliable operation of such cooling systems isof critical importance, particularly, of course, when passengers are tobe transported in the vehicle. Failure or malfunction of a coolingsystem, e.g., during an abnormally fast reentry or during heat build-upover an extended period of time, could result in the occurrence ofuncorrectable damage to vital elements of a craft and mean the loss ofpassengers and vehicle alike. It is highly desirable, therefore, tominimize the complexity of such cooling systems and to eliminatecomponents such as pumps, sensors, and hydraulic control systems, etc.which may be subject to malfunction under high-stress conditions. Asspace travel becomes more routine, it becomes increasingly desirablethat space craft be capable of repeated usage rather than single flightsonly. To achieve this end, effective means for cooling the vehicle uponreentry, which means may be replenished after a flight for repeatedusage, is essential.

It is accordingly, a major object of the present invention to provide anew and improved cooling system for a vehicle subject to aerodynamicheating.

Another object is to provide such a system which is operable in responseto the rate of aerodynamic heating occurring at a given time.

Another major object is to provide a heat-responsive cooling system ofreliable and efficient operation which obviates the necessity ofmechanical or electrical control systems, pumps, sensors, and the like.

Yet another object is to provide such a system which may be convenientlyand inexpensively refurbished and filled with coolant following use.

Yet another object is to provide such a system which is operable toprotect multiple areas of a vehicle which are subject to varying degreesof heating.

A further object is to provide such a system which is of simpleconstruction, and of practicable and inexpensive manufacture. 1

Other objects and advantages will be apparent from the specification andclaims and from the accompanying drawing illustrative of the invention.

In the drawing:

FIG. 1 is a longitudinal, partially sectioned, somewhat diagrammaticview of a missile nose section employing a first embodiment of thecooling system;

FIG. 2 is a view, similar to FIG. 1, showing the expandable material ofthe cooling system in an enlarged configuration;

FIG. 3 is a fragmentary, sectional view, on an enlarged scale, of aportion of the porous body of FIG. 1 and showing the external coating;

FIG. 4 is a longitudinal, sectional view of the forward portion of themissile nose section showing a modification of the first embodiment ofthe cooling system;

FIG. 5 is a view, similar to FIG. 1, showing a second embodiment of thecooling system;

FIG. 6 is a view, similar to FIG. 2, illustrating the second embodimentand showing the expandable material in an enlarged configuration;

FIG. 7 is a longitudinal, sectional view of a missil nose sectioncontaining a third embodiment of the cooling system;

FIG. 8 is an isometric, diagrammatic view of portions of a wingstructure employing a modification of the cooling system and withportions of the tank cut away:

FIG. 9 is a cross-sectional, diagrammatic view of a portion of thestructure of FIG. 8; and

FIG. 10 is a view, similar to FIG. 9, of a modification of the systemshown in FIGS. 8 and 9.

With initial reference to FIG. 1, an embodiment of the cooling system 10is employed in the nose section 11 of a missile adapted to reenter theatmosphere of the earth at high velocity and which is thus subject to intense aerodynamic heating during reentry. The missile nose section 11 isof conical configuration and has an external skin 12 of a material, suchas beryllium, chosen for its superior strength and durability whensubjected to extremely high temperatures. A frustoconical chamber 13 isdefined within the nose section 11 adjacent at least a portion of anarea of the skin 12 which area is subject to intense aerodynamicheating; the chamber 13 is preferably at least partially defined by theinner surface of the skin 12. The chamber 13 is also partially definedby a bulkhead 14 ex-tending transversely of the longitudinal axis of thenose section 11 and defining the rear of the chamber 13. The forwardportion of the chamber 13 is defined, in the preferred embodiment, bythe base of a conical, porous body 15, described more fully below, whichconstitutes the forward portion of the nose section 11.

As illustrated in FIG. 1, the chamber 13 is partially filled with acoolant 18, the coolant being chosen from tion of 53944 grain-calories/gram afidTa/hich also pro- 5 vides good blockage of heat flow andradiation when ejected into the boundary layer adjacent the nose section11, as will be more fully described. In addition to liquid coolants suchas water, certain normally solid materials are also suitable, providedthey have a range of vaporization temperatures below the temperature atwhich operation of the cooling systems is desired. For example,polytetrafluoroethylene has a vaporization temperature of 867 K and aheat of vaporization of 378 gram calories/gram at atmospheric pressureand thus can be utilized when operation of the system is not necessaryat lower temperatures.

Also contained within the chamber 13 is a means for increasing thepressure within the chamber upon being heated by energy produced byaerodynamic heating of the vehicle and comprising a quantity ofheatexpandable material 19. The expandable material 19 is a materialhaving a thermal coefficient of expansion substantially greater thanthat of the coolant 18 and is a material adapted to expand substantiallyfrom its original configuration while in a non-vaporized state and attemperatures below those at which the outer skin 12 begins to looseintegrity of construction; silicone rubber, for example, is a preferredmaterial because of its high linear coefficient of expansion ofapproximately 6.7 X IO in/inF. If water is used as the coolant 18, it isdesirable that the expandable material 19 be resilient and rubberlike inconsistency to permit compression thereof in accomodation of expansionof the coolant 18 in the event of its freezing when the missile oraircraft is exposed to subfreezing temperatures during, for example,high altitude flight and while outside the atmosphere of the earth.

As shown in FIG. 1, the expandable material 19, in its initial ornon-expanded configuration, comprises a layer of material seated againstthe external skin 12 of the nose section 11 and preferably bonded to theinner surface of the skin 12. The expandable material 19 is thus oftapered external configuration, of annular cross-sectionalconfiguration, and constitutes an annular layer of material whichpartially encloses the coolant 18. In the present embodiment, theexpandable material 19 is preferably molded into place by beingintroduced, in uncured, liquid form, into the chamber 13 as the nosesection 11 is spun about its longitudinal axis, thus obtaining anaxisymmetrical distribution of the expandable material within the nosesection 11 and en suring consistent bonding of the material to the innersurface of the skin 12.

The conical, porous body 15 is rigidly joined, e.g., suitably welded, tothe external skin 12 at the forward portion of the skin. The porous body15 has an external surface configured to extend contiguously of theexternal surface of the remainder of the nose section 11. The materialof the porous body 15 is one which is not easily deformed at the hightemperatures encountered during reentry, and suitable materials includecarbon derivatives and boron and stainless steel. A preferred processfor its manufacture which is commonly em- 5 ployed in the art in thesintering of particles of a matebody 15 and the skin 12, it may bedesirable to provide reinforcement of the juncture, as illustrated inthe modification of FIG. 4, because of the difficulty of obtaining agood weld. An externally threaded sleeve 16, of an external diameterless than the internal diameter of the forward portion of the skin 12,is rigidly seated within a corresponding, annular, cutout section formedcoaxially of the base of the porous body 15. In the present example, theinner surface of the sleeve 16 tapers inwardly in a forward directionand the sleeve is joined to the porous body 15 by sintering the body inplace within the sleeve 16. The forward portion of the skin 12 of thenose section 11 is provided with corresponding internal threads 17 topermit threading engagement of the nose section 11 with the sleeve 16.The nose section 11 may additionally be bolted or pinned (not shown) tothe porous body 15.

The porosity of the porous body 15 is determined by the size of theparticles and the amount of variation of the sizes of the particles. Theporosity should be sufficient to permit seepage through the porous body15 of a small amount of the coolant 18in liquid form but to preventsignificant passage therethrough of liquid coolant, and to permitpassage of the coolant upon its being converted to a vaporized stateduring aerodynamic heating of the nose section 11. An alternative methodof construction of the porous body 15 is to employ a plurality of finescreens formed of filaments of high fusion point materials such as boronor stainless steel, the screens being pressed and bonded or fusedtogether, one upon the other, to provide a desired thickness andporosity. The junction of the porous body 15 and the outer skin 12 thusdefines an outlet 21 (FIG. 1) for the chamber 13, and the outlet 2l andthe porous body 15 comprise a means for conducting coolant to theexternal surface of the skin 12 of the nose section 11 by transpirationof the coolant through the porous material. Any coolant conductedthrough the porous body 15 is thus ejected over the forward portion ofthe nose section 11 adjacent the leading area of the skin 12, which isthe portion subject to the greatest aerodynamic heatmg.

Means are provided for normally preventingpassage of the coolant 18 fromthe chamber 13 to the external surface of the porous body 15 andof theskin 12; in the present embodiment, a coating 22 (FIG. 3) is depositedover the external surface of the porous body 15, the coating being of amaterial having a melting point below that at which operation of thecooling system is desired. Solder is a suitable material, as is epoxyresin. The coating 22 seals the external surface of the porous body andserves to prevent seepage or evaporation of the coolant 18 duringstorage of the nose section 11, but is of a sufficiently low meltingpoint to ensure melting of the coating during heating of the nosesection 11 above a predetermined temperature at which operation of thecooling system 10 is desired. Alternatively, a diaphragm orpressure-relief valve (not shown) isinstalled in series with the outlet21 for permitting passage of coolant 18 upon pressure within the chamber13 being raised abovea predetermined level during aerodynamic heating ofthe nose section 11.

In operation, the protective coating 22 prevents passage of coolantthrough the porous body 15 during storage of the missile and duringinitial flight of the velicle at speeds below those at which significantaerodynamic heating occurs. During high-speed flight through theatmosphere or during reentry, greatly increased air pressures occuradjacent the leading portions of the craft, and stagnational andfrictional reaction of the airflow with the nose section 1 1 causesaerodynamic heating of forward portions of the craft. As the temperatureof the nose section 11 increases, the temperatures of the skin 12 andthe porous body 15 also increase, and substantial heat flux is conductedfrom the heated exterior portions to the chamber 13 and theheatexpandable material 19 within the chamber. The expandable material19 and the coolant 18 initially act as a heat sink to absorb anddisperse heat from the porous body 15 and skin 12 throughout theremainder of the nose section 11. As the temperature within the chamber13 continues to rise, the expandable material 19 expands and increasesthe pressure within the closed chamber 13. Upon the temperature of thecoating 22 reaching the melting point, the coating melts and isdispersed by the airflow adjacent the nose section 11, permittingpassage of fluid through the porous body 15. In

the preferred embodiment wherein water is used as the coolant 18, thetemperature reached by the porous body 15 during operation of thecooling system 10 is sufficient to vaporize substantially all the waterupon contact or during passage of the coolant through the porous body,thus permitting more rapid ejection of the fluid, in the form of steam,through the porous body 15. vaporization of the water which occurswithin the chamber l3 and porous body 15 provides substantial cooling ofthe nose section 11 because of the relatively high latent heat ofvaporization of water.

With reference to FIG. 2, the expandable material 19 has expandedinwardly to substantially fill the chamber 13, and the coolant 18 hasbeen substantially dissipated through the porous body 15. The coolantdispersed outwardly through the porous body 15 is swept rearwardly overthe porous body 15 and the skin 12 of the nose section 11 in thedirection represented by arrows 27, producing a layer of air andvaporized coolant adjacent the skin 12 which acts to cool the skin 12and to shield it from very hot gasses which are produced around the nosesection 1 1 by radia'tional and frictional reaction of the forwardportion of the nose with the hypervelocity airflow. The cooling system10 thus utilizes the coolant l8 first as a heat sink to absorb anddisperse heat throughout the nose section 11, secondly as an evaporativecooling means, as the coolant is vaporized during its ejection throughthe heated, porous body 15, and thirdly as a vapor layer, surroundingthe skin 12, which protects the nose section 11 by blockage of thesuper-heated gasses surrounding the nose section 11. The heat-expandablematerial 19 provides the important advantage, when the system iscompared with cooling systems employing evaporation alone to eject thecoolant, of increasing the pressure within the chamber and therebycausing ejection of the coolant 18 through the porous body 15 beforedangerous heating of the nose section-l1 occurs, This occurs because theexpandable material 19 begins to expand and exhaust the coolant 18 whenexposed to temperatures below those at which significant evaporationpressure occurs, and below temperatures at which dangerous heating ofthe skin 12 and other portions of the nose section 11 occur. Moreover,the expandable material 19 serves to extend the period of ejection ofcoolant, and to prevent brief, wasteful surges of pressure and resultantcoolant ejection during intense heating, by continuously decreasing thevolume available to the coolant as the coolant is evaporated and ejectedand thus continuously maintaining increased pressure within the chamberfor ejecting the coolant. Absent the expandable material 19, thepressure produced by evaporation of the coolant during heating isinitially great, but decreases rapidly as the coolant is ejected and thevapor is permitted to expand throughout the volume.remaining in thechamber 13.

With reference to FIG. 4, the modification of the first embodimentincludes a length of perforated tube 23 which is tightly fitted within abore 24 formed coaxially within the porous body 15 from its base andextending forwardly from its base as far as is possible withoutsignificantly weakening the forward end of the porous body. Theperforated tube 23 extends rearwardly to the rear bulkhead 14 and issuitably supported by being welded or otherwise affixed to the bulkhead.An additional, solid, tapered rod 25, of a material having stability andstructural integrity when heated, is tightly fitted within the forwardend of the perforated tube 23. The tapered rod 25 extends forwardly fromthe perforated tube 23 within a corresponding, forwardly tapered cavity26 also formed coaxially within the porous body 15 and extendingsubstantially to the tip of the porous body. The perforated tube.23serves to enhance circulation of the coolant 18 from the chamber 13 tothe porous body 15 and permits more consistent distribution of thecoolant throughout the porous body 15. The presence of the projectingelement 25 and perforated tube 23 within the porous body 15substantially increases the strength of the body 15, and reinforces itsattachment to skin 12, to help it resist the stresses of reentry. Duringthe final stages of expansion of the expandable material 19, theperforated tube 23 permits free circulation of coolant 18 from allportions of the chamber 13 and prevents the expandable material 19 fromclosing upon itself and isolating pockets of unused coolant 18.

With reference to FIG. 5, a second embodiment of the cooling system Aalso employs a heatexpandable structure 19A and a coolant 18 adapted tobe ejected through a porous body during aerodynamic heating of the nosesection 11, but the expandable structure 19A is disposed centrally ofthe chamber 13A, and the coolant 18 is disposed externally of theexpandable structure 19A and adjacent at least portions of the skin 12which are subject to aerodynamic heating, i.e., between these portionsand the expandable structure 19A. The expandable structure 19A comprisesa plurality of sheets of expandable material wrapped one upon the otherin annular, concentrai array and disposed coaxially of the longitudinalaxis of the nose section 11. This layered construction preventsundesirable stresses within the expandable structure in the event thatone portion is heated at a different rate than another portion. Suchinconsistent heating may cause uneven expansion of the structure, whichcould cause sealing off of portions of the chamber 14A when one portionof the expandable material reaches the outer skin 12. The rear bulkhead14A, modified from the first embodiment, is formed as a cone extendingforwardly in and coaxially of the nose section 11 and within theexpandable structure 19A. The second embodiment, by containing thecoolant 18 adjacent the heat-receiving, external skin 12 rather thanwithin the expandable material 19, provides a faster response to heatingof the nose section 11 because the coolant is in contact with theexternal skin 12, whereas in the first embodiment of FIGS. 1 and 2, theexpandable material 19 acts as an insulating media and reduces initialheating of the coolant 18. This may cause a delay in the response of thesystem when water is used as a coolant and becomes frozen during flight.The second embodiment of FIGS. 5 and 6 is preferred for use in missileshaving very high reentry speeds or which experience very rapid heatingand thus require a cooling system having almost immediate response. Thesecond embodiment operates similarly to the first embodiment, butdiffers in that the coolant 18 is in direct contact with the heated skin12 and is thus heated and evaporated at an earlier stage of theoperation of the system, the expandable structure 19A being expandedsomewhat later. Initially upon heating, a quantity of coolant adjacentthe outer skin 12 is quickly heated to evaporation and ejected byevaporative pressure. As shown in FIG. 6, as the expandable structure19A is heated, it enlarges outwardly, and coolant is urged forwardly andflows between the expandable material 19A and the outer skin 12 to theporous body 15, where it is ejected as in the first embodiment.

With reference to FIG. 7, a third embodiment 10B of the cooling systemis generally preferred for solving the heating problems of vehicleshaving average reentry velocities. The cooling system 103 is alsoemployed within the nose section 11 of a missile subject to aerodynamicheating. As in the first two embodiments, a coolant chamber 13B isdefined within the nose section 11 and contains a coolant and anexpandable material. A circular, first or primary bulkhead 14B definesthe rear of the chamber 13B as in the first embodiment of FIGS. 1 and 2.In this third embodiment, however, the expandable material is in theform of an open-celled, or substantially open-celled, sponge-likematerial which is impregnated with coolant, the impregnated, opencelledmaterial being shown at 29. The expandable, open-celled material 29preferably is foamed, silicone rubber, suitably formed in place bymixing unvulcanized, silicone rubber with a chemical blowing agent, suchas N, N dinitrosopentamethylene tetramine, and heating the mixture atvulcanizing temperature and according to processes known in the art.

At the forward portion of the nose section 11 a conical, porous body 15Bis affixed, at its base, to the outer skin 12 and extends forwardly andcontiguously therefrom, as in the first two embodiments. In theparticular form illustrated in this third embodiment, the porous body158 is hollowed rather than solid and is formed of porous material ofapproximately the same thickness as the adjacent outer skin 12. Thus, acavity 28 of approximately conical configuration is formed within theporous body 158 for collecting vaporized coolant and distributing itevenly through the porous body 153. A baffle 30, suitably ofsubstantially flat, annular configuration, is mounted within the nosesection 11 adjacent and to the rear of the porous body 15B and extendsacross the nose section perpendicularly of the nose section major axis.The baffle 30 is affixed continuously along its periphery to the outerskin 12 and serves to isolate the cavity 28 from the expandable material29. An imperforate conduit 32 extends between the baffle 30 and theprimary bulkhead 14B and is disposed approximately coaxially of the nosesection 11, the conduit extending within corresponding bores formedcoaxially through the baffle 30 and the bulkhead 14B and being welded orotherwise rigidly affixed within at least one of the corresponding boresand sealingly fitted within the other. A secondary bulkhead 33 ofcircular configuration is affixed, at its periphery, to the outer skin12 at a location spaced rearwardly from the first bulkhead 14B andextends parallel to the first bulkhead and transversely of the nosesection 11, thus defining a manifold chamber 34 between the first andsecondary bulkheads. The first bulkhead 14B has a plurality of orifices35 formed therethrough for providing communication between the coolantchamber 138 and the manifold chamber 34. A plurality of perforated tubes36 are tightly fitted within respective ones of the bores 35 through theprimary bulkhead 14B and extend forwardly, within the chamber 138, forproviding improved circulation betweenthe various portions of thechamber 138 and the manifold chamber 34. The exemplary embodiment ofFIG. 7 also includes an additional, ablative layer 37 bonded to theexterior of the outer skin 37 within an indented portion of the outerskin 12 which indented portion extends rearwardly from the approximatelongitudinal center of the chamber 138. The ablative, outer layer 37 isof a material such as nylon phenolic head shield material and isemployed for providing additional protection from intense heating ofportions of the outer skin 12 which are spaced a distance outside thearea, adjacent to the porous body 158, which is most efficiently cooledby the present cooling system 108, as described below.

An inlet into the chamber 138 is provided for permitting initialinjection of coolant, and is suitably formed through the secondarybulkhead 33 and normally closed by a cap 38 threadingly engaged therein.

In operation, the third embodiment 108 (FIG. 7) functions similarly tothe first and second embodiments in that heat absorbed by the outer skin12 and the porous body 158 causes enlargement of the expandable material29 and evaporation of the coolant. Expansion of the material 29increases fluid pressure within the chamber 138, and fluid coolant iscaused to flow from and through the open cells of the sponge-like,expandable material'29. However, the coolant, while in liquid form, isprevented from flowing in a forward direction by the baffle' 30 and theconduit 32 and is also discouraged from rearward flow by deceleration ofthe missile during reentry. Upon reaching a vaporized state, the coolantis under increased pressure but is free to flow in a rearward directiononly; it is thus passed through the perforated tubes 36 and the orifices35 and into the manifold chamber 34. From thence the vaporized coolantflows forwardly through the imperforate conduit 32 to the cavity 28 andis then passed through the porous body by transpiration to providecooling of the external surfaces of the nose section 11 as in theprevious embodiments. The baffle 30, manifold chamber 34, and conduit32, by causing the coolant to recirculate rearwardly in vaporized formbefore reaching the porous body 158, prevent wasteful usage of coolantin liquid form caused by sudden deceleration forces during reentry. Thatis, coolant which is suddenly urged in a relative forward directionwithin the vehicle by inertial forces during reentry is prevented frombeing ejected too quickly through the porous body B, but rather isretained to first absorb a substantial quantity of heat from the skin 12until changed to a vaporous state in which it is thencirculatedthroughthe manifold chamher 34 and conduit 32 at a moreuniform rate. Thus, the ejection of coolant is extended over a longerperiod of time and provides increased thermal protection. Theopen-celled, expandable material 29 serves to attentuate any undesiredperiodic movement or *sloshing" of the coolant within the chamber 13Bwhich may tend to affect the stability of the space craft.

With reference now to FIG. 8, a modification of the above-described,open-celled embodiment is employed as a cooling system 10C withina.seg-ment of a wing 39 of a vehicle such as a space shuttle orspace/air vehicle (not shown) used for both aerodynamic flight throughthe atmosphere and rocket-powered flight beyond the atmosphere. Onedesign concept for such a craft, referred to as a low-cross-rangedesign, requires that the vehicle enter the atmosphere and deceleraterapidly in the upper atmosphere (by reentering ata high angle of attack)to avoid excessive heat buildup and preserve the structural integrity ofthe craft. It is possible that the vehicle can accomplish reentrywithout the expenditure of a liquid coolant if vhigh temperatureresistant materials are used in the leading edges. However, it isconsidered necessary that a liquid cooling system be installed andmaintained in readiness for use if the vehicle experiences abnormalheating because of reentry at excessive velocity or for other emergencyconditions such as spalling of the heatshield. With added reference toFIG. 9, an elongated tank 40 is fitted within the wing 39 and parallelto the leading edge of the wing 39, the tank 40 defining a chamber 13Ccontaining opencelled, expandable material impregnated with coolant, theimpregnated, expandable material being represented at 29. The tank 40 issuitably seated against and within the outer skin 12C of the wing 39. Aplurality of perforated tubes 36C are contained within the chamber 13Cfor enhancing circulation of the coolant throughout the expandablematerial 29, the perforated tubes 36C suitable being affixed to endwalls41 of the wing segment and extending axially of the tank 40. Theperforated tubes 36C communicate with each other through intermediateconduits 42, and with a single, outlet conduit 43. With referencespecifically to FIG. 9, a pressure relief valve 44 is mounted within theoutlet conduit 43 and is operable for preventing fluid flow through theoutlet conduit 43 from the perforated tubes 36C unless a predeterminedpressure is applied to the valve 44. The outlet conduit 43 communicates,at its outlet end (i.e., its end opposite the end connected to theperforated tubes 36C) with an imperforate distribution tube 48 whichextends parallel to the perforated tubes 36C and adjacent the wingleading edge, shown as the leftward portion of the wing 39 as viewed inFIGS. 8 and 9 of the drawing. A plurality of outlet tubes 49 extend fromthe distribution tube 48 forwardly toward the leading edge of the wing39, extend in sealing association with the tank 40 through correspondingopenings formed through the tank 40, and are seated withincorresponding, annular cavities 50 (FIG. 9) formed within the outer skin12C. The outlet tubes 49 are mutually spaced along the length of thewing 39. Thin portions 51 of the outer skin 12C extend across thebottoms of the respective cavities 50, and the cavities 50 aresufficiently deep to permit rupture of these thin, remaining portions 51upon the passage of coolant through the pressure relief valve 44 andconduit 43. Alternatively, replaceable blowout plugs (not shown) aretightly fitted within the respective cavities 50. The pressure reliefvalve 44 acts to normally prevent passage of coolant to the outlet tubes49. The endwalls 41 of the tank 40 are preferably of a constructionthinner and less substantial than the walls of the remaining portion ofthe tank 40, for reasons which will become apparent from the descriptionto follow. Inlet openings (not shown) are suitable formed in the tank 40for permitting replenishment of the coolant after use.

In operation, the cooling system C of FIGS. 8 and 9 serves as a meansfor distributing heat from the leading edge of the wing 39 throughoutthe tank 40 during routine operation of the space/air craft whenabnormal heating is not experienced The external skin 12C dissipatesheat by radiation to the external environment. Heat conducted to thecoolant-impregnated, expandable material 29 in the tank 40 causes someincrease in pressure within the tank 40 as occurs in the third em-'bodiment, of FIG. 7, but the pressure is not sufficient to open thepressure relief valve 44, and coolant is thus prevented from exitingfrom the tank 40. Upon the occurrence of excessive heating which causesthe pressure within the tank 40 to exceed the predetermined level atwhich the valve 44 opens, however, coolant under high pressure isconducted through the outlet conduit 43, the distribution tube 48, andthe outlet tubes 49. The coolant under high pressure within the outlettubes 49 ruptures the outer skin 12C at the reduced portions 51 acrossthe respective cavities 50, and coolant is ejected through the skin 12Cto provide protective cooling of the heated area as in the otherembodiments. The pressure within the chamber 13C then decreases somewhatas the chamber is cooled by the coolant. As the coolant pressure-inchamber 13C decreases due to the cooling effects of the ejected coolanton the outer skin 12C, the relief valve 44 will begin to close and thusconserve the coolant, i.e., the relief valve 44 also functions as aregulating valve that controls the mass flow of coolant in proportion tothe heat load on skin 12C.

While the cooling system 10C, as thus far described, is effective forprotecting only one segment of the wing 39, in use a plurality (notshown) of chambers 13C are mounted adjacent one another along the lengthof the wing 10C, each being adjacent a portion of the leading edge ofthe wing 39 for providing protection to the respective, adjacent portionof the wing. Each cooling system 10C also includes the heat-expandable,coolantimpregnated material 29 for increasing the pressure within therespective chamber 13C upon being heated by aerodynamic heating of theportion of the leading edge of the wing 39 which is adjacent therespective chamber 13C. Each system 10C includes a respective, pressurerelief valve 44 for normally preventing passage of coolant to theadjacent portion of the external surface of the skin 12C and forpermitting passage upon the occurrence of excessive, deleterious heatingof the respective, adjacent portion of the skin 12C. Thus, shouldexcessive heating occur chiefly adjacent only one of the cooling systems10C, the tank 40 of that system is first exhausted without wastingcoolant from the other systems. Then, if the pressure within the systemsadjacent, i.e., on either side of, the exhausted tank I 40 has notincreased sufficiently to cause opening of the relief valve 44 of therespective adjacent system, pressure in the respective adjacent systemis exerted against the respective, common sidewall 41 and ruptures thesidewall, allowing coolant from the adjacent cooling system to flow intothe tank 40 of the exhausted system 10C and provide additional coolantfor the dangerously heated area of the skin 12C adjacent the exhaustedcooling system 10C. Alternatively, pressure relief valves or diaphragms(not shown) may be employed for providing emergency communicationbetween respective, adjacent tanks 40. The perforated tubes 36C ofadjacent tank 40 may be open ended, and the tubes of one tank connectedwith those of the adjacent tanks but separated by a diaphragm or reliefvalve adapted to open upon exhaustion of coolant from one of the tanks40, as in the modification of FIG. 10 to be described below.

With respect now to the modification shown in FIG. 10, the principle ofsegmented, mutually adjacent tanks is employed with respect to first andsecond chambers 13D and 13E which are vertically spaced, as well asspaced along the length of the wing 39 as in the modification of FIGS. 8and 9. A partition 52 separates the two adjacent chambers 13D, 13E. Animperforate, connecting tube 55 extends between and communicates withthe perforated tubes 53, 54 of the respective chambers 13D and 13E. Theconnecting tube 55 extends through a corresponding bore through thepartition 52 and is sealingly associated with the partition 52. Adiaphragm 56 is extended across the connecting tube 55 for normallypreventing fluid flow therethrough. Upon the exhaustion of coolant ineither one of the chambers 13D, 13E, the pressure within the exhaustedchamber decreases relative to that in the other chamber, and thepressure differential created across the diaphragm 56 causes it torupture, thus allowing coolant to flow through the connecting tube 55from the adjacent chamber to partially replenish the exhausted chamber.Outlet tubes 49A and 49B communicate, respectively, with perforatedtubes 53 and 54 and operate as do the outlet tubes 49 of themodification of FIGS. 8 and 9 to disperse coolant to the respective,adjacent, potentially severely heated areas of the outer skin 128. Firstand second pressure-relief diaphragms 57 and 58 extend across theinterior of the first and second outlet conduits 49A, 498, respectively,to prevent passage of coolant through the respective outlet conduits tothe skin 12C until a predetermined chamber pressure is reached and thusfunction in a manner analogous to the operation of the relief valve 44(FIG. 9). The modification of FIG. 10 is effective to conduct coolant toa respective, vertically defined portion of the leading edge of the wing39. The modification of FIG. 10 is operable when one such verticalportion is abnormally heated during reentry at an angle of attack whichcauses heating of the particular, respective portion, e.g., by increasedstagnation occurring at a particular angular section of the leadingedge.

With respect to each of the above-described embodiments, it is evidentthat the cooling system provides operation in direct response to therate of aerodynamic heating occurring at a given time and thus minimizesany waste of coolant before operation is required. Moreover, the systemis of straightforward, relatively simple construction when compared withprior-art devices, and completely eliminates the necessity of pumps,sensors, timing mechanisms, electrical circuits and the like which havebeen used in analogous prior devices. Reliability of operation is thusimproved by the elimination of breakdowns of such mechanisms.

I atmospheric flight, the vehicle having an external skin at least aportion of which is subject to aerodynamic heating, the apparatuscomprising:

a chamber defined within the vehicle adjacent a portion of the skinwhich portion is subject to aerodynamic heating;

a coolant partially filling the chamber;

heat-expandable means, comprising a material also contained within thechamber and expandable while in a non-vaporized state, for expanding,increasing the pressure, and progressively reducing the volume availableto the coolant within the chamber upon being heated by energy producedby aerodynamic heating of the vehicle; means, communicating between thechamber and the external surface of the skin ata leading area of theportion of the skin subject to aerodynamic heating, for conductingcoolant to the external surface of the skin upon the pressure within thechamber being increased by the heat-expandable means; and

means for normally preventing passage of coolant from the chamber to theexternal surface of the skin and for permitting passage of coolant tothe external surface upon the occurrence of aerodynamic heating of thevehicle above a predetermined level. 1

2. The apparatus of claim 1, wherein the chamber is at least partiallydefined by the inner surface of the portion of the skin subject toaerodynamic heating.

3. The apparatus of claim 1, wherein the means for conducting coolant tothe external surface of the skin comprises a means for conductingcoolant to the external surface of the skin by transpiration of thecoolant through a bodyof porous material.

4. The apparatus of claim 3, wherein the body of porous material has anexternal surface contiguous with the external surface of the skin, andwherein the means for normally preventing passage of coolant from thechamber to the external surface of the skin and for permitting passageof the coolant upon the occurrence of aerodynamic heating of the vehicleabove a predetermined level comprises a coating normally sealing theexternal surface of the body of porous material, the coating having amelting point below the preselected temperature.

5. The apparatus of claim 3, wherein the vehicle constitutes a missilehaving a forward nose section, and wherein the body of porous materialconstitutes the forward portion of the nose of the missile, wherebycoolant ejected through the body of porous material during aerodynamicheating of the missile is carried rearwardly adjacent the externalsurface of the missile by the adjacent airflow for cooling the missile.

6. The apparatus of claim 1, wherein the heatexpandable means comprisesa quantity of a heatexpandable material having a coefficient of thermalexpansion substantially greater than that of the coolant.

7. The apparatus of claim 6, wherein the heatexpandable material isdisposed adjacent portions of the periphery of the chamber and betweensaid portions of the periphery of the chamber and the coolant. 3. Theapparatus of claim 6, wherein the coolant is disposed adjacent portionsof the periphery of the chamber and between said portions of theperiphery of the chamber and the heat-expandable material.

9. The apparatus of claim 6, wherein the heatexpandable material is aresilient, rubberlike material.

10. The apparatus of claim 9, wherein the heatexpandable material issilicone rubber.

11. The apparatus of claim 9, wherein the heat expandable material is anopen-celled, spongelike material which is impregnated with the coolant,the impregnated, heat-expandable material substantially filling thechamber.

12. The apparatus of claim 11, the chamber being provided with an outletcommunicating with the means for conducting coolant to the externalsurface of the skin, the apparatus further comprising at least oneperforated tube contained within the chamber and communicating with thechamber outlet.

13. The apparatus of claim 12, wherein the means for conducting coolantto the external surface of the skin comprises a means for conductingcoolant to the external surface of the skin by transpiration of thecoolant through a body of porous material, and wherein at least oneperforated tube is provided in communication with the chamber andextending within the body of porous material.

1. Apparatus for cooLing a vehicle during high-speed, atmosphericflight, the vehicle having an external skin at least a portion of whichis subject to aerodynamic heating, the apparatus comprising: a chamberdefined within the vehicle adjacent a portion of the skin which portionis subject to aerodynamic heating; a coolant partially filling thechamber; heat-expandable means, comprising a material also containedwithin the chamber and expandable while in a non-vaporized state, forexpanding, increasing the pressure, and progressively reducing thevolume available to the coolant within the chamber upon being heated byenergy produced by aerodynamic heating of the vehicle; means,communicating between the chamber and the external surface of the skinat a leading area of the portion of the skin subject to aerodynamicheating, for conducting coolant to the external surface of the skin uponthe pressure within the chamber being increased by the heat-expandablemeans; and means for normally preventing passage of coolant from thechamber to the external surface of the skin and for permitting passageof coolant to the external surface upon the occurrence of aerodynamicheating of the vehicle above a predetermined level.
 2. The apparatus ofclaim 1, wherein the chamber is at least partially defined by the innersurface of the portion of the skin subject to aerodynamic heating. 3.The apparatus of claim 1, wherein the means for conducting coolant tothe external surface of the skin comprises a means for conductingcoolant to the external surface of the skin by transpiration of thecoolant through a body of porous material.
 4. The apparatus of claim 3,wherein the body of porous material has an external surface contiguouswith the external surface of the skin, and wherein the means fornormally preventing passage of coolant from the chamber to the externalsurface of the skin and for permitting passage of the coolant upon theoccurrence of aerodynamic heating of the vehicle above a predeterminedlevel comprises a coating normally sealing the external surface of thebody of porous material, the coating having a melting point below thepreselected temperature.
 5. The apparatus of claim 3, wherein thevehicle constitutes a missile having a forward nose section, and whereinthe body of porous material constitutes the forward portion of the noseof the missile, whereby coolant ejected through the body of porousmaterial during aerodynamic heating of the missile is carried rearwardlyadjacent the external surface of the missile by the adjacent airflow forcooling the missile.
 6. The apparatus of claim 1, wherein theheat-expandable means comprises a quantity of a heat-expandable materialhaving a coefficient of thermal expansion substantially greater thanthat of the coolant.
 7. The apparatus of claim 6, wherein theheat-expandable material is disposed adjacent portions of the peripheryof the chamber and between said portions of the periphery of the chamberand the coolant.
 8. The apparatus of claim 6, wherein the coolant isdisposed adjacent portions of the periphery of the chamber and betweensaid portions of the periphery of the chamber and the heat-expandablematerial.
 9. The apparatus of claim 6, wherein the heat-expandablematerial is a resilient, rubberlike material.
 10. The apparatus of claim9, wherein the heat-expandable material is silicone rubber.
 11. Theapparatus of claim 9, wherein the heat-expandable material is anopen-celled, spongelike material which is impregnated with the coolant,the impregnated, heat-expandable material substantially filling thechamber.
 12. The apparatus of claim 11, the chamber being provided withan outlet communicating with the means for conducting coolant to theexternal surface of the skin, the apparatus further comprising at leastone perforated tube contained within the chamber and communicating withthe chamber outlet.
 13. The apparatus of claim 12, wherein the means forconducting coolant to the exteRnal surface of the skin comprises a meansfor conducting coolant to the external surface of the skin bytranspiration of the coolant through a body of porous material, andwherein at least one perforated tube is provided in communication withthe chamber and extending within the body of porous material.